text:
Would a helicopter with the blades on the bottom fly the same, if at all?
I've heard that the pendulum rocket fallacy applies to rotorcraft as well. As stated above, I'm curious to know if a helicopter with blades on the bottom of the body would experience any effects from this. (Yes I know it's impractical and landing would be terribly difficult.)

Given the practical difficulties in such a configuration, it's unlikely you'll find a full-sized built version.  But fixed-wing aircraft fly very similarly whether high-wing or low-wing.  Maybe there's a drone version out there you could fly upside down.

@mms That seems right if the helicopter blades counter-rotate to point "up and down" as the craft wobbles.  But if they rotate with the craft?  Imagine the craft rotates 45 degrees from vertical; the rotor thrust doesn't "pull it vertical", it just pulls it towards 45 degrees.  There is no torque towards vertical unless you turn the helicopter blades away from the axis of symmetry of the craft.

Somehow this question reminds me of a completely unrelated question.

@Mast yes, it makes a huge difference if the rotor actually rotates.

Yes that is possible, like the Hiller flying platform demonstrated. It had two counter-rotating propellers inside a shroud and the pilot controlled his craft by shifting his body weight, like on a Segway. There is no law of physics that prohibits a helicopter from flying upside down.

The Hiller flying platform was one of several types built in the 1950s, after it was observed that controlling an underslung rotorcraft by weight shift could be learned by untrained personnel in 20 minutes. The DeLackner Aerocycle was another platform built based on this finding. The idea was later abandoned due to practical issues like kicking up rocks into the rotor blades, and an at the time unexplainable interference between the counter-rotating blades. The Aerocycle had a fixed rotor head, the dynamics of which were poorly understood at the time.
For full scale helicopters, having the rotor underneath the helicopter has the same stabilising effect on flight characteristics. Stability of helicopters (and of fixed wing aircraft) is studied from the perspective of aerodynamics: the effects of wind gusts or control inputs.
In the hover, the speed stability ${\delta M}/{\delta{\dot{x}}}$ plays a significant role: if positive, the hover is unstable. A human can learn how to control an unstable platform if the time period of the oscillation is high enough (conventional helicopter pilot), but it is much easier to fly in an aerodynamically stable aircraft (the underslung platforms intended for general infantry personnel). The speed stability effect in the hover equates to a gust of wind blowing from directly forward, does then the change in moment tend to amplify or counteract the effects of the gust. This can be visualised like so:
Image source
The gust blowing on the helicopter tilts the rotor back, which tilts the thrust vector. A teetering conventional rotor has a positive ${\delta M}/{\delta{\dot{x}}}$: it wants to flip backwards ever stronger, and is therefore aerodynamically unstable in the hover. An underslung teetering rotor has a moment change that stabilises: it tilts the fuselage back, and due to aerodynamic coupling the rotor follows back to neutral. A rotor with hinge offset has a smaller stabilising moment, but a stronger fuselage/rotor coupling.
So to answer your original questions: Yes the helicopter with an underslung rotor would fly, and it would be easier to control than a conventional helicopter. It is just a bit unpractical, that's all.

The main problem is rather pilot / passenger might accidentally step into a rotor that is below them instead of above them.

@mins One other thing I can think of as to why we might not see many of these flying around is the stability concerns. Helicopters with the body of the craft under the 'wing' will have a centre-of-gravity lower that the 'lift-point'. In the case that you cannot generate lift and start plummeting downwards, gravity will keep the body below the wing and keep it stable during auto-rotation. However, I am sure someone could design the under-wing version with that stability in mind.

@MichaelCoxon and that is exactly the pendulum rocket fallacy that the OP mentions in his question. With a fully articulated rotor head, as long as the rotor rotates the body will follow the plane of the rotor disk, whether the rotor is under or above the body.

There's also the Airgeep and Avrocar.

An under-slung rotor would also prevent the biggest uses of a heli over a plane. and that is the ability to lift and lower loads under the aircraft. That is how we rescue injured people from boats, the water, cliffs and other steep/treacherous terrain. As well as carry everything imaginable into places that roads were never built into.

@RowanHawkins Yeah, it’s a bit unpractical,

We spend all our weekends mowing lawn with these guys.

Courtesy: Helifreak.com
You can find thousands of Youtube videos showing how comfortably they can do that

They sure have different limitations than the full scale ones  but then the question is broadly about how a helicopter will react when the rotors are at the bottom and imho this fits in perfectly for an explanation without taking away anything from the big ones. These helis can sustain inverted flight for as long as they have juice

Without a wider shot of the background, I'm tempted to say that this is an upside-up helicopter whose photo has been flipped =P.

@E.P. I'm not sure what you mean. The photograph hasn't been mirrored, as you c an see from the writing on it. The background is clearly the right way up: there's grass at the bottom, with a fence visible behind and above that (on the right-hand edge, behind the rotor) and trees behind and above that, tapering upwards as you'd expect.

@DavidRicherby I'm not sure I'd say that the right-way-up-ness of the background is anywhere near that obvious, but my comment wasn't a serious suggestion either.

I assume that for this the angle of the blades is opposite to what they would be if the helicopter was the right way up

Yes it is, for inverted flights rotor blades do change into negative pitch

If you have any doubts about the physics of a helicopter being able to fly with the rotors under the body, here's  a video that that happening. https://youtu.be/Qrmd_Qdryos?t=228 Yes the stunts are impossible for anything larger than an model, but it demonstrates that the rotors can be beneath the craft with no more stabilization needed than with the rotors above the body of the helicopter

If your lawnmower is flying, you may be doing it wrong.

I've been flying 3D/aerobatic helicopters since before the computer-aided stabilizers came on the scene. For a naturally stabilized helicopter, they are a little unstable when inverted. Having the CG below the blades gives a "dihedral" action that tends to want to return the helicopter to level flight, if the machine is balanced. Being inverted does the opposite of that - the machine wants to return to the low-energy state of fuselage below blades. Computer gyro (flybarless) systems compensate for that with control inputs, but that natural instability is still there.

One of the first helicopters that really flew (c. 1918) was the 'Petróczy-Kármán-Žurovec', intended to be used by the Austro-Hungarian Army as a tethered observation platform. The observer stood above the contra-rotating rotors...
(Image source)
http://www.aviastar.org/helicopters_eng/petroczy.php

Not bad, but two comments: "this captive observation helicopter", so the problem of balancing is actually avoided due to the cable(s) which holds the aircraft vertical; and we don't know if the center of gravity is really above the rotor.

Also, there is clearly a lot of mass below the rotor counterbalancing the observation platform - i.e. three engines, apparently.

As far as I understand the aerodynamics and dynamics of a rotor wings and disk, it would actually be more stable, at least at some degree, regarding blow back of the rotor disk. Since the CG of such helicopter would be above the rotor disk. Rotor disk/blade aerodynamics are not that straight forward and you have a lot of other forces involved depending on the phase of the flight. I'll try to elaborate more, when I get to the computer.
After finding my notes, interesting enough, only talks about rotor above CG condition, in hover. It states:

"(...) rotor alone, above the CG, is dynamically unstable in hover!
Hovering dynamic instability problem:
In case of an horizontal velocity disturbance:

flapping angle appears;
flapping angle appears;
rotor and thrust are tilted;
horizontal acceleration is installed;
horizontal velocity builds up untill rotor flapps in the opposite direction;

The process is repeated in the opposite direction with increasing
  amplitude!
For large helicopters, the hovering oscillation period is usually long
  enough for safe reaction of the pilot."

It also talks about de Lackner HZ-1 Aerocycle:
https://en.wikipedia.org/wiki/De_Lackner_HZ-1_Aerocycle
When you are flying forward, there is a blow back force, produced by the advancing blade, creating lift, which then reflects 90° due to gyroscopic precession. This make the rotor disk to blow back, that is why when you fly helicopters you are always pushing the cyclic forward, more and more with velocity (this means, more lift created by the advancing blade, due to the increased relative wind).
This is the only reason I am saying that it would be more stable, because the helicopter would have a tendency, in the nose dive, to blow back the disk, thus decreasing the angle of attack of the advancing blade. In the case of helicopters, this also happens, which in turn they need a horizontal stabilizer in the tail, to counter the nose down attitude.
I don't know if I am making any sense, it is really hard to explain all the dynamics involved, but there are some good books regarding the matter of helicopter aerodynamics.

Why would having the CG above the disk make a difference to stability?

@CarlKevinson as I said above, as soon as I get the opportunity I'll elaborate more on the subject. I remember a few years ago, a professor from helicopter dynamics, talking about this. It is not a simple answer, it involves a lot more than just the Center of Mass and Center of Pressure. It also involves forces that are acting upon the rotor disk, depending on the phase of flight. I will try to look for my books on this subject and elaborate more later.

@mins well... stick to a phase of flight. Stability changes depending on the phase of flight. If you want to study a rotor disk, you have to study it depending if it is hovering, ascending or descending powered, horizontal flight or autorotative flight. I am no expert in helicopter dynamics. I am a helicopter pilot with and aeronautical engineer degree, but no specialization in aerodynamics. What I can do, is try to answer accordingly with the material I have. As soon as I get a more complete answer, I will reply to you. But basically, it depends on the phase of flight.

A way to simplify the presentation of a helicopter with the rotor assembly on the bottom is to consider the lift created by the rotors as buoyancy and therefore create a direct comparison to a ship/boat.  The described helicopter would demonstrate negative static stability (regardless of your discipline).  As the center of lift moves away from the center of gravity (think of an extreme: a 30' vertical pole with a horizontal force at the top), no force exists naturally to return the system to equilibrium.  The lift created by the rotors is now through a line perpendicular to the plane of the rotors. When the rotors are above the center of gravity, the vertical force of gravity drives the center of gravity below the center of lift (or center of buoyancy in the ship example).  hope this helps.

A ship does not flip over though, does it. My updated answer contains an explanation of what happens in a helicopter in the hover.

Reverse blade pitch and it should push instead of pull you up. No landing gear would be my problem. I'm a helo mechanic not engineer just to be clear.

To much collective up would cause the blades to strike the aircraft if they worked like normal. An inverted helo flies down so reverse the pitch not rotation

Blades rise into a more conical shape when gaining altitude if you stay with a normal configuration you hit the aircraft. And still no landing gear

You didn't say inverted you said under the aircraft

@Derek Ues there would be all kimds of practical problems with placimg the rotor underneath.. You could assemble all your points into an answer to this question

I never said that flying with the main rotor beneath the aircraft wasn't possible but show me how to land.

the issue that isnt being adressed by these "engineers" is stability. lower rotor/tall mass mass aircraft are heavily affected by small movements of the mass above the rotor, taller rotor/lower level mass aircraft dont have this issue due to the fact that changes in mass position do not affect the vector of the thrust to mass position in the same manner as it does when the payload is above the rotor. this was proven by the navy and the airforce with their "lifting platforms" that utilized thrust from below the  pilots. the other issue is the fact that these craft used liquid fueled internal combustion engines which also caused mass changes  due to fuel use, which destabilized mass distribution.    Electric model choppers and drones dont use liquid fuelwhich shifts as the craft shifts from upright to upside down.  In short there are multiple laws of physics that work against low rotor position air craft.

Electric Model helicopters are a recent entry, Nitro Helis have been here for decades and can do the same

https://www.youtube.com/watch?v=Qrmd_Qdryos&feature=youtu.be&t=228

you could try being a little less condescending when speaking of people you don't know.

Yawn. Aways a bore to meet a repository of all wisdom.


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Can high-bypass turbofans cruise at high altitude?
They have talked for years about re-engining the B-52 with something more modern than its TF33-P-3/JT3D turbofans, which are fairly low-bypass (1.42:1 for the JT3D).
Modern engines are much higher bypass - like the GE Passport at 5.6:1, similar to the CF34 - in the same weight class and thrust as the TF33.   A larger engine like the LEAP has an even higher bypass ratio, e.g. 11:1.
Now, the B-52 has a published operating ceiling of 50,000 feet.  The 737, A320, Bombardier RJs etc. have a ceiling of 41,000.
However the KC-135s, re-engined with semi-modern CFM56 high-bypass turbofans, have a ceiling of 50,000 feet.
So I am confused. Does the bypass ratio have an impact on the practical ceiling of the aircraft?  Could the B-52 fly to current spec with engines like the GE Passport?
A side question... the TF33 claims a specific fuel consumption of 0.56 lb(lbf-h).  I can't seem to find that figure on the most recent high-bypass turbofans.  Is it inapplicable to high-bypass turbofans?  If not, is there a viable way to figure what a modern engine would do to the B-52's range?

Yes in principle, but some modifications are advisable.
What limits the maximum operating altitude of a jet engine (besides the thrust needed to climb up there) is the length of the combustion chamber and the absolute pressure of the air entering it. Since the atmospheric pressure drops with altitude and the compression ratio of the compressor stays constant, the absolute pressure in the combustion chamber drops with altitude.
For combustion to take place, first the fuel droplets injected into the air stream need to evaporate. This is made easier by higher temperature and pressure, and the lower both are, the more residence time of the fuel-air mixture (caution, PPT link) in the combustor is required for good combustion. Longer combustors have higher pressure losses and weigh more, so engine designers try to limit their length.
Just throttling down can already cause the ignition to stop at high altitude. If a flame-out occurs, the engine cools down quickly and a restart at a lower altitude might not be possible. Turbofans suitable for high altitude operations use special measures to stabilize the flame. When they are in place, there is no reason the B-52 can't continue to fly at 50,000 ft.

If we define thrust T of a turbofan as
$$ T = \dot{m} \cdot (V_e - V_0)$$
with:

$\dot{m}$ = total mass flow through both the gas generator and the fan
$V_e$ = average exhaust speed
$V_0$ = airspeed

we can see that thrust is proportional to mass flow. At higher altitude the air density is lower, so mass flow through the engine is lower, but as long as combustion can be maintained, the engine at altitude can still deliver a fraction of its sea level thrust. This fraction needs to be sufficient to propel the aircraft at cruise speed of course, plus excess climbing power for reaching the cruise altitude, so TO thrust needs to be sufficient for this. Just a matter of dimensioning the engine.
The operational ceiling of an aircraft is a function of the wing geometry: wing loading, aspect ratio, wing profile, taper ratio, twist. For a given aircraft that is re-engined, operational ceiling would not change.
The bypass engine is powered by a gas generator, identical to a single stream turbojet - the higher bypass engine operational limits are the same as those for a single stream turbojet.

Although of course the engines will be important in allowing an aircraft to reach its service ceiling, the choice of service ceiling has more to do with the aircraft than the engines in this case.
Airliners are designed to to be economical to operate. Flying higher puts more stress on the fuselage to maintain the same cabin pressure. To guard against the higher risks in the case of decompression, regulations regarding emergency oxygen supplies may have higher requirements for aircraft flying this high. Peter discusses the issues in engine design for these altitudes. All of these costs are just not worth any benefits of flying higher. See also: Why are many jet aircraft designed to cruise around FL350-370?, including another good answer from Peter.
Military aircraft are designed to different requirements. They will not accumulate flight cycles nearly as fast as an airliner, reducing stress put on the fuselage. In the case of the B-52, only the crewed areas in the forward fuselage are pressurized, reducing the amount of reinforcement needed. Thus the costs are lower, and military aircraft have more emphasis on performance, providing the incentive for higher ceilings. Business jets have the same low-cycle high-performance requirements.
You mention the CFM56 and GE Passport. As you note, the 737 and A320 use the CFM56 engine and have lower ceilings, while the KC-135R has a ceiling of 50,000 feet. The GE Passport powers the Bombardier Global 7000/8000 which have service ceilings of 51,000 feet. So there is no reason to doubt that high bypass turbofans can function at these altitudes.
Thrust Specific Fuel Consumption (TSFC) is very dependent on conditions. It's available if spend some time looking but you have to be careful that you are comparing the same conditions. This site lists military aircraft engines. The JT3D/TF33 of the original KC-135 and the B-52 is around 0.535 lb(lbf-h). The F108-CF-100 on the KC-135R is listed at 0.363 lb(lbf-h).
This table lists specs for commercial jet engines.

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What is this white-tail, short upper deck 747 I just saw?
It was seen taking off from a US Air Force base, which is part of Air Mobility Command.  A great deal of their operation is departing or returning troops from abroad, so it gets a lot of rare visits from oddball commercial aircraft.
This 747 had the short 3-window upper deck area, so it was a -100,-200 or SP, and it wasn't an SP.    It was a "white tail", entirely white except for some numeric markings.
No USAF marking, that's not a surprise since the Air Force has six 747-100/200s: all accounted for by four NEACP planes (why would they come to an AMC base?) and two VIP transports (and they have a distinctive paint scheme, so, I wouldn't be asking).
It did not carry the distinctive markings of several Arab state head-of-state aircraft, the NASA paint scheme, nor the Las Vegas Sands Corp. scheme, nor Earnest Angley Ministries.   It did not have any funny engines on it.  Kalitta Air doesn't fly them anymore.
I have to assume none of the nine in Iranian service would be visiting a USAF/AMC base.
I'm sorry, I tried to get a photo, but could not safely stop.  What could this airplane be?

Maybe Flightradar can help? Funny engines :D

@ymb1 I did not know the 400F had a short bump.  I also can't imagine why they'd use a contractor freight-only bird when the base is lousy with C-5s and C-17s.  Much of the movements there seem to be passenger, so I assumed it was a passenger plane.

Did it have winglets?  If so, -400F.

The Ukrainians probably hacked the Russian computers and got their order of Iranian drones delivered to a USAFB.

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text:
Could the S.H.I.E.L.D. C-17 actually have a sensible center of gravity?
In a question about whether tail surfaces add to lift, I thought of a fictional example where the tail surface very much adds to lift: The Agents of S.H.I.E.L.D C-17, highly modified and super-engined.  Presumably the T-tail vertical stabilizer (still present) provides downforce for trim, and the aft wing provides lift; though that wouldn't necessarily have to be so.
And my first reaction was "The center of gravity on this would be totally unworkable." But is that really true?

I mean, it looks like the rear wing would account for about 20% of lift, maybe a tick more because it is being blown by the forward engines.  So if you marked the main-wing center of lift and the aft-wing center of lift, the aircraft CG would need to be inside that range, about 20% aft of main-wing.
Would that put the CG aft of the rearmost landing gear wheel?  Wouldn't it "pop a wheelie" the moment they lost elevator authority?
But then, if their Stark/Asgard/Tesseract tech can get 150,000 lbf out of a PW2000, maybe they can move the landing gear aft.
If you haven't seen Agents of Shield, spoiler alert...

  One hat-trick that aircraft can do is "tip the engines up" and go into full VTOL.
The cattywumpus angle of some of the engines are dynamic adjustments for station keeping; this is obvious in the video.

 That seems to place some very particular demands on Center of Gravity,  noting that the engine lift is significantly forward of wing lift.  Especially when you fail an engine - worst case being a tail engine.  Presumably, everything is specced so a single engine rollback in VTOL/hover mode could be easily compensated for. Clearly, that would factor into CG also, as the loss of a tail engine would be the worst case, necessitating the CG stay fairly forward.

 Would the CG for forward flight be compatible with the CG for vertical hover?

Related

You're putting a lot of faith in TV/movie CGI groups to actually get aerodynamics and flight dynamics right. Especially in the spoiler'd comments.

that rear "wing" seems worse than useless. The airflow disturbance from the engines and turbulent air departing the wing proper would cause havoc, and the very fact of it being there would adversely affect its pitch characteristics something serious.

Other problem is they park Coulson's Vette and their giant SUV on the tail cargo door, adding to more rear-ward weight.

Might have been better as a canard design.  Yes, you can have two wings bearing weight with the CG in between.  But the fore wing must stall first.  This C17 would have problems unless there was a lot of weight up front, or if the rear wing(s) stalled first.  But note that the extra engines could go on the main wing, or the second wing could be mounted above or below the first, or even in front, making it an Avanti Piaggio from hell.  This design actually might have a chance if the T tail was removed as the transport version of the B-58 Hustler.
But for the movies, this design will certainly do.

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Are altimeters calibrated to ISA geopotential altitude or ISA geometric altitude?
Altimeters convert a pressure measurement to an indication of altitude. When set to standard pressure setting (1013.25 hPa / 29.92"Hg), they assume the atmosphere is according to the ICAO Standard Atmosphere (ISA) and indicate the altitude accordingly. However, ISA has two altitude definitions; geometric altitude and geopotential altitude.
The ICAO Standard Atmosphere is a model of the atmosphere up to 80 kilometres high, based on the perfect gas law and the hydrostatic equation.  In order to deal with the effects of reduction of gravity with height, it uses the concept of geopotential altitude H:
$$H= \frac{1}{g_0}\int_0^hgdh$$
with:

$h = \textrm{geometric altitude}$
$H = \textrm{geopotential altitude}$
$g_0 = 9.80665\textrm{ m/s, mean gravitational acceleration at mean sea level}$
$g = \textrm{local acceleration of gravity (height dependent)}$

Gravity is given by :
$$g = g_0 \left(\frac{r_e}{r_e + z}\right)^2$$
with:

$r_e = \textrm{the radius of the earth}$

And thus the relation between geopotential altitude and geometric altitude is given by:
$$H = h\frac{r_e}{r_e+h}$$
And
$$h = H\frac{r_e}{r_e-H}$$
In the ISA model, the properties of the atmosphere (pressure, temperature, density) are all calculated with respect to geopotential height.
For a geopotential height of 12 500 meters (41 010.5 ft), which corresponds to a geometric height of 12524.6 meters (41091.3 ft), the ICAO atmosphere gives a pressure of 178.648 hPa.
My question is: what will a perfectly calibrated altimeter indicate when the pressure is 178.648 hPa? Does it indicate 41 010.5 ft (the geopotential altitude) or does it indicate 41091.3 ft (the geometric altitude)?
You might say that the difference is "only" 80 feet, but for RVSM operations that is quite significant.
The ICAO standard atmosphere (as described in ICAO Doc 7488) does not give the answer (at least I couldn't find it). And it includes tables for every 500 meters of both geopotential and geometric altitude, so that does not make it easier.
I'd like to know which altitude is indicated on an altimeter (ISA geopotential or ISA geometric) and where (in which official document) this is specified.

Following the U.S. Standard Atmosphere 1976, 178.648 hPa (mbar) yields a pressure altitude of 41010.5 ft

@selectstriker2 Like the ICAO atmosphere, the US Standard Atmosphere 1976 yields both 41010.5 ft (geopotential) and 41091.3 ft (geometric). The calculations are the same, and the tabular data is provided for both geopotential and geometric data.

I guess I should have stated that a calibrated TSO C106 altimeter should provide that altitude. @Gerry's answer is quite correct as to the driving document for that determination

Even if I didn't know the correct answer, I would strongly suspect it was geopotential altitude. With respect to it (H), pressure distribution is simpler and calculations are easier - particularly important when they have to be implemented on a mechanical device. One needs additional correction to convert to geometric altitude.

The TSO for Air Data Computers is TSO-C106. It specifies for the minimum performance standard "SAE Aerospace Standard 8002, Air Data Computer - Minimum Performance Standard."
From AS8002:

3.6 Altitude Reference:
Calibration of the static air sensing mechanism for pressure altitude
  outputs (including baro-corrected if supplied) shall be to the
  geopotential altitude tables of U.S. Standard Atmosphere, 1976.

While this is a US standard, the FAA asserts it is in compliance with ICAO Doc 7488.
For RVSM, additional requirements are levied against the installation primarily focused on reduction of static source error (SSE). That guidance is available in AC 91-85A.
It's important to remember that absolute accuracy at altitude is not as important as everyone adhering to the same reference.

Thank you for the quote from AS8002, exactly what I was looking for. Also the European equivalent (ETSO-C106) refers to SAE AS8002.

In addition to the great answer provided by @Gerry, altimeters certified under TSO C10b (revised 1959) aren't required to be as precise. These are generally older analog altimeters. They must meet AS392C, which provides a table of values per NACA Report 1235, as well as tolerances.
The tolerance at 187.54 mbar (40,000 ft) is $\pm$ 230 ft!
C10 was revised to C, which requires the altimeter meet AS 8009C, Pressure Altimeter Systems, dated May 24, 2016.

4.4.1 Altitude Pressure Values
Altitude pressure values shall be in accordance with U.S. Standard Atmosphere, 1976 (Reference ICAO Standard Atmosphere Document 7488).

It also states that differential pressure calibration for SSEC should adhere to NASA Technical Note D-822, which does specify geopotential altitude:

Within an atmospheric layer throughout which the molecular scale temperature is a linear function of geopotential altitude, the hydrostatic equation and the perfect gas law yield the following expressions for pressure...
...
Pressure-altitude tables are given for altitudes up to 30 000 geopotential meters.

Thanks for the extra info on TSO C10b. Would highly appreciate it if you or anybody else could find the relevant quote from AS8009C like in Gerry's answer for AS8002.

It doesn't look like AS 8009C specifies geopotential or geometric

Does it refer to an atmosphere standard, or does it just provide a table?

it differs from AS 392C (which provides the pressure next to the altitude) in that it only has Test Pressure Altitudes, which correspond to a given tolerance

Modern air data systems are calibrated to geopotential height. That is, at some given pressure, the altimeter reads the geopotential altitude associated with that pressure in a standard atmosphere.
I doubt that any of us has ever flown in a standard atmosphere, therefore the altimeter reading we see is a pressure altitude associated with the non-standard atmosphere in which we find ourselves. You can't really know your actual geopotential height unless you also know the exact temperature profile from some datum to your position. And, if you have that temperature profile information, it can be quite tedious to determine your geopotential height.
As was mentioned elsewhere, none of this really matters as long as we all have the same Kollsman number set and obstruction clearance is not a factor.
Lower altitudes at low temperatures can require a prudent correction to published altitudes in order to maintain obstacle clearance.
(Derivations provided upon request)
Ed Lambert, PE
ATP A320, B747-4, DC9

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text:
Is aluminum electrical wire used on aircraft?
Aluminum electrical wire got a bit of a bad reputation in household wiring due to reacting badly with terminals not properly rated for aluminum.  Properly handled, it works fine, but it's so distrusted for small branch circuits that distributors won't even stock it.
Aluminum is a worse conductor than copper, by almost half. But that only considers it by volume (e.g. Wire diameter).  By mass, the advantage swings back to aluminum.  Nearly twice the ampacity for the same weight.  Where would that matter?  Aircraft.
Transport class aircraft are increasingly electrical, like the bleedless 787 where electrical does much of the heavy lifting.
Is aluminum wire actively used in aviation?  Or is it "taboo" like it is with houses?

Probably even more taboo than with houses, as aluminum doesn't handle vibrations very well. Copper is more ductile.

I suggest you read up on the whole A380 wiring saga back in 2005, as it involved aluminium wiring...

@kebs https://www.popularmechanics.com/flight/a982/4201627/ http://www.us-tech.com/RelId/1425875/pagenum/2/ISvars/default/The_Benefits_of_Using_Aluminum_as_a_Conductor.htm http://www.cadalyst.com/cad/product-design/what-grounded-airbus-a380-10903 http://old.seattletimes.com/html/businesstechnology/2003131857_webeads16.html https://www.prysmiangroup.com/en/products-and-solution/references/transportation-and-mobility/30%25-weight-saving-with-aluminium-wires

Also note that like a car, there's no return wiring on an aircraft. It's done through the aluminum structure of the aircraft. (Article here on how they do it on carbon fiber fuselages)

Cable is not just the metal wire. It's also insulation, installation, cable channels, extra space at tight bends where cable flexibility is insufficient, and maintenance of said cable. Aluminum corrodes in a lot of conditions and happens to be one of the most fatigue-susceptible metals.
For these reasons, most aircraft wiring is copper and silver-plated or nickel-plated copper. Such wiring is reliable even under imperfect conditions.
But there are cases where different considerations prevail. Sometimes it's just the need to have some minimum cable thickness, for mechanical and handling reasons. Other times it's a thick bus bar where weight makes a difference and quality is easy to ensure.
So beside copper there is some steel, copper-nickel plated aluminum, copper-nickel plated steel, and pure aluminum wiring in aircraft.
In aircraft, safety is ensured and validated with engineering and testing; risks of the kind one can take with home wiring are not accepted. The price of aluminum wire is installation and maintenance complexity instead. The ends need to be cleaned and crimped or welded, sometimes the aluminum wire is terminated with a bimetallic insert. As a result, aluminum wiring is more expensive than copper, not less. It will likely require more maintenance work in the future.
Until recently, aluminum has been mostly avoided for these reasons, and used only for thick wires and bus bars. Currently there is enough confidence in quality management and maintenance that aluminum wiring is getting more use in attempts to save some weight, the A380 in particular uses aluminum wires up to 22 AWG. Such weight savings come at the cost of more parts and more work, both in production and later in service.
Specific percentages vary widely, but generally non-copper wiring accounts for more than 10% and less than 50% of overall wire weight in a production commercial aircraft.

"...risks of the kind one can take with home wiring are not accepted..." Ouch. :-)

As far as relative risk goes, in aviation, there is a lot of quality control and inspection - from manufacturing to routine maintenance. Issues that might develop over time should be caught during inspections. In domestic application, there is a lot of do-it-yourself installation of variable quality that can easily go uninspected until the house burns down. It's more important to go with the "ever reliable" in domestic use. In aviation, it doesn't have to be "ever reliable", provided developing issues can be caught and corrected during scheduled inspections.

Al isn't just used for bus bars: the A320 forward, 757/767/747-400, L-1011, and the MD-11 all use Al feeder wiring. In terms of small aircraft, Piper and Cessna both used it for a while. The new technology, seen in the A380, is to cold weld large connections, not crimp.

Cessna Cardinals used it to connect battery in the tail to where ever if goes up front.
The ends were properly terminated and treated to prevent dissimilar metal corrosion.
My 1973 plane is still flying with it.


text:
When to go missed on a non-precision approach?
I am training to get my instrument rating and I have come across a confusing point.   I understand that, when flying a precision approach, you go missed upon reaching the decision height for that approach if visual reference to the runway environment is insufficient to complete the landing.   I also understand that on a non precision approach you will descend to the minimum decision altitude for that approach and then fly at that altitude until you reach the missed approach point, after which you will go missed.   My question is, how do you know when you've reached the missed approach point on a non-precision approach?
These three charts in particular confuse me:

In this approach, which has an option for either an ILS (precision) or LOC/DME (non-precision) approach, the beginning of the dotted line which signifies the missed approach path does not have any DME value or intersection information.   There is an intersection after it at 7.5 DME.   Which of these two points would be the missed approach point for the LOC/DME approach?   How would you know when you reached the MAP if it is where the dotted line begins?
(Click to view)

In this approach the dotted line which signifies the missed approach path seems to begin at the runway threshold.   If this were the MAP, (with no localizer) would you have to start a timer after you cross KOLLI intersection to know you have gone 2.4nm and thus are over the runway threshold?   Is the MAP actually at the beginning of the runway as it seems?   Are there any ways of knowing you are at the MAP without a stopwatch?
(Click to view)

Finally, this IAP is similar to the first.   Unlike the first though, there is no DME intersection after or near the beginning of the dotted missed approach line.   Is the MAP for the localizer approach here just at the beginning of the runway as it seems to be in the second approach?   Again, would you have to use a stopwatch or are there any other ways?
(Click to view)

Non precision MAP fixes are identified in a number of ways:

Fixes identified by additional terrestrial Navaids eg intersections between the localizer and radial directions from other Navaid beacons like VORs, NDBs, etc..
Fixes identified by DME slant ranges.
Fixes identified by flying a linear course from an identified FAF at a specific airspeed for a specific time.
Fixes identified by area navigation systems.
Fixes identified by specific GNSS waypoints (RNAV GPS).

For the ILS or LOC/DME rwy 5 KCGZ, when flying the LOC/DME, Your MAP is on localizer at MDA at 7.5 NM DME from the Stanfield (TFD) VORTAC.  There is no other means using the equipment required to fly this approach procedure to identify the MAP.
For the LOC rwy 22 into KCDW, your MAP is on localizer at or above MDA when you cross the threshold of rwy 22.  Flying the approach at the correct category airspeed, you can also time it using the table in the lower left corner of the plate.  But the plate clearly says that the MAP is 5.4 NM from the FAF.
For the ILS or LOC 1 into KILG, the LOC rwy 1 MAP is again on localizer at MDA when the aircraft crosses the threshold of rwy 1.  This is defined by the approach timetable on the lower right of the plate.

Ah, I didn't see those timetables.   That makes sense.   However, are you sure the MAP is that last waypoint (TFD 7.5) for the first approach?   How do you know it is not the runway threshold as it is in the approach brought up in this question: https://aviation.stackexchange.com/questions/21437/how-to-determine-the-map-for-an-rnav-mda-approach

Yes.  There is no other means available to identify the MAP otherwise.

So whenever there's an intersection after the precision MAP on a precision/np approach plate the MAP is not over the runway threshold but is at that intersection? What if the FAA wanted the MAP for the np approach to be before the MAP for the precision approach? If it is just marked with an intersection, how would you know that an intersection before the precision MAP was not the np MAP?   Why isn't this made clearer?   It is especially ambiguous on ILS or LOC/DME approaches because you don't have a time table to verify the np MAP.   Isn't this dangerous?

The position of the MAP on a non-precision approach is specific to the approach being flown; there is no hard and fast rule like that to follow.  Again the best way to determine where the MAP is by thoroughly briefing the approach plate during flight planning and again before entering the terminal environment.  It’s not dangerous as long as you understand what is going on here.

Ok. I still wish they made it a bit clearer whether in the first approach whether the LOC/DME MAP was 7.5 or 7.8 dme but I guess you just have to use common sense - that they wouldn't include an intersection that didn't define a lower altitude or the FAF for the np approach that WASN'T the MAP. Also I don't think they would ever put the np MAP before the glideslope MAP on np/p plates because obstacle clearance in that area would already be assured for the glideslope app and they might as well give the np approach a better chance to see the runway by sending them closer (since they are higher).

I realize this post is 5 years old but hopefully I can clarify for someone down the road.  I’m 30+ years instrument rated, former CFI, 20+ years ATP mil and civil and I myself looked this up today…life happens.
In the mil they always foot-stomped reading the title of the approach to determine minimum equipment required to legally fly it.  The title always indicates required equipment to fly from FAF to MAP; nothing more.  So it’s up to us to determine if and how we can fly full segment (prior to FAF) and the published MAP.  If not properly equipped, you must request alternate means.  This is typically RADAR vectors to intercept FAF and then heading/altitude for vectors as alternate MAP.
To the OP question, LOC/DME Rwy 5; LOC/DME in title and absence of timing table was the clue.
Also, compare timing table FAF to MAP distance to profile view of approach procedure.
Tip—include runway exit gameplan to approach brief because this is a horrible time to reference plate.
Another tip—after years of vector to ILS full stop, your full segment and MAP skills will go to crap.  Focus on this.
Every airport is surveyed for surroundings and approaches are tailored for available equipment, terrain, traffic count, etc and this is why approaches, especially non-precision approaches, are so you unique.
Fly safe!

To clarify your answer a bit, the title of the procedure refers to the lateral guidance on final. The FAA has moved away from including “DME” in the title, instead opting to place that in the equipment requirement box located in the pilot briefing bar. You should expect to see “ILS or LOC RWY XX” as the title and “DME required.” in the pilot briefing bar when it is required anywhere from the IAF through the published missed approach procedure.

Timbo, you are correct.  Thanks for adding that.


text:
Why does indicated airspeed change with altitude?
I know that if you fly at a low altitude and at a high altitude at the same TAS, your IAS will be lower at the high altitude than at the low altitude.   Why is this though?   Wouldn't the static vent account for the change in pressure?   I have heard it has to do with the change in density but why would this effect the system as it measures pressure not density?   Maybe because ram air pressure (measured by the pitot tube) is affected by density?

As you state, IAS is simply based upon the difference between total pressure and static pressure. For low subsonic conditions:
$$ p_t = p_s + p_q = p_s + \frac {1}{2} \cdot \rho \cdot V^2$$
$\rho$ is the air density, which is a function of air temperature: $\rho = \frac {p_s}{R \cdot T}$. For indicated airspeed, the density at sea level $\rho_{SL}$ at 15 degC is taken:
$$ V_i = \sqrt {\frac{2 \cdot (p_t - p_s)}{\rho_{SL}}}$$
However, the actual dynamic pressure measured by the pitot tube is caused by actual density.

When temperature decreases, density increases.
So at colder temperatures, some of the dynamic pressure is due to higher $\rho$
Therefore, the $V_{ind}$ bit decreases. The pitot only measures dynamic pressure and does not know what is due to temperature

Air is colder at higher altitude if we stay in the troposphere - climb to over 33,000 ft and the IAS does not change anymore.

The anemometer is not a true speed instrument, but returns the value of the dynamic pressure at the Pitot tube, that can be correlated with the airspeed only for a given density. Thus, at higher altitudes, (lower air density) airspeed has to be higher in order to generate the same dynamic pressure at the Pitot tube, and the opposite is true for lower altitudes (higher density) where airspeed has to be lower in order to generate the same dynamic pressure...

Your airspeed is measured as a difference in pressure between the pitot (ram air) and static ports. As you go up in altitude the amount of air entering the pitot tube decreases even though the true airspeed stays the same. This reduces the "pressure" seen by the airspeed indicator and therefore decreases the delta seen between the two ports, indicating a lower airspeed.

But wouldn't the static port also see less air and compensate for it?   Why does the pitot tube sense this but not the static port?

of course, they both sense less air. But the delta between them is also less. Hence a lower IAS will be indicated

@Murey Tasroc   The values at both static and Pitot are both absolute pressures, the sum of static and dynamic pressures. At the static port, the dynamic pressure is zero, and the static pressure is the same as the static pressure at the Pitot. Hence, and as the anemometer gives you the difference in absolute pressures between the pitot and the static port, that difference amounts to the dynamic pressure only...

True airspeed does not stay the same as altitude increases unless power is reduced in which case the airplane is flying at a higher angle of attack and a lower indicated airspeed.

This bothered me as well with most of the explanations I found online, until I remembered that the pitot tube measures dynamic PLUS static pressure.
This makes sense when you remember that the pitot tube is also open to the outside air pressure just like the static vent.
As such, at higher altitudes the static vent will receive less pressure due to the drop in static air pressure, but the pitot tube will receive even less for two reasons; the drop in both static and dynamic air pressure.
Hope that helps.
This youtube video helped me when trying to answer your question:

No math is needed to explain.
If you fly at 100 knots indicated and climb from 1,000ft to 5,000ft with the same power your indicated airspeed will remain about the same.
In order to fly at the same true airspeed, you’d have to reduce power. So true airspeed is only constant if you make changes to your flight configuration to make it constant- it’s really not constant at all. Even if you stay at the same altitude, if the temp changes, it will change.


text:
What could cause a low-pressure compressor first stage blade of a turbofan engine to bend forward?
What could cause a low-pressure compressor first stage blade of a low-bypass turbofan engine to bend forward?
I also noticed rotor path rubbing in the 9 to 12 o'clock portion (while usually this can happen only in the 6 o'clock area).

You should provide more context to ease the reading of your question.

also, can you post a picture?

Not a great deal I think is the answer so if you have one it's a bit worrying. How much is it bent by and where (tip/root)? Pictures would be very helpful!

Is it specifically the leading edge of the tip of the blade that is bend forward?

And welcome to Aviation.SE, Anso.

Also it's worth noting that on some compressor blade tips the leading edge is deliberately bent slight forward. Hence why a picture would be useful.

Sorry guys i cannot provide image because it is confidential data. There is no sign of FOD though. the bending of the blades is almost same as your first image. I suspect that the abradable coating in rotor path came chipped off (as a  large piece, but it cannot be confirmed because the rubbed area doesn't look so) because of any ovality in casing and it might have struck in between blades and rotor path. Total 5 blades got bended. first in the five got more damage and the following ones got less bend.

Forward bending of the first stage of the low pressure compressor is usually associated with (soft) Foreign Object Damage (FOD).
Ice and/or large quantities of snow in the engine intake will typically cause forward bending of the leading edge of the tip of the blades.

 Damage to GE CF680C2 turbine engine compressor fan blades after snow/ice ingestion
Source: Flight Safety Australia

 Damage to Turbomeca gas turbine Arriel 2B turbine engine compressor blades after snow/ice ingestion
Source: Transport Safety Board of Canada, aviation accident investigation report A12P0008

Thank you for the answer. There is no sign of FOD though. the bending of the blades is almost same as your first image. I suspect that the abradable coating in rotor path came chipped off (as a  large piece, but it cannot be confirmed because the rubbed area doesn't look so) because of any ovality in casing and it might have struck in between blades and rotor path. Total 5 blades got bended. first in the five got more damage and the following ones got less bend.

@AnsoMamachan: Blade bending is a sign of FOD.


text:
Did/do any commercial passenger aircraft have showers for passenger's use?
The Emirates A380 has a shower unit for use by First class passengers (previously discussed here), but it got me thinking about the many passenger comforts present in the "golden age" of aviation (pre-US airline industry deregulation, especially when piano lounges were a thing in 747 aircraft) - did any other commercial passenger aircraft (jets or otherwise) have onboard showers for the benefit of passengers?
If not, it seems surprising, because a toilet room could easily be converted to a wet-room shower unit - and aircraft have a ready supply of potable water. Showers could be time-limited to a few minutes - enough to freshen-up after a long-haul flight and I can see it would be popular with business travelers who might not have the luxury of time to use their airlines' business class lounge's showers.

Personally I think the limitations on water use due to supply and the difficulties of showering in anything but smooth air make the prospect unappealing. Just trying to whiz while standing up can be a huge challenge on an airplane at times.

I highly recommend we not to abuse the word "aircraft" in this SE. If you mean airplane, say airplane.

Good point @user3528438, I'm sure Zeppelins had showers.

I wonder if this would comply with safety rules like when crossing a turbulence area and everyone should be seated, specially with bare feet on slippery material.

@mins: Bare feet on slippery material shouldn't be a problem if you have good shower mats.

@GdD: Yes, at least one of them did.

If you're including lighter-than-air aircraft, the LZ 129 Hindenburg had showers:

B Deck on Hindenburg, located directly below A Deck, contained the ship’s kitchen, passenger toilet and shower facilities, the crew and officers’ mess, and a cabin occupied by Chief Steward Heinrich Kubis (containing a door to the keel corridor, which was the only connection between passenger and crew spaces).

My emphasis.

On Emirates or Etihad long haul flights, they do have showers available only to certain passengers. Here you can find a link to an article about the showers. After those two airlines, as for inflight showers go, I do not know of any other inflight showers.
The 777 has inflight showers as well. The airline can request the systems necessary to have the showers. So technically any plane can have it.

The A380 was noted in the OP. The question was looking for any other airplane that had in-flight shower facilities.


text:
What safety rule replaced the now-rescinded two-person rule (after Germanwings 9525)?
In the aftermath of Germanwings 9525 in 2015 many airlines instituted a two-person rule for the cockpit (aka "two-man rule") - with a flight-attendant replacing whichever pilot left the flight-deck.
In 2017 the industry rescinded that rule. Articles about the repeal of the rules don't mention what alternative processes are being used to prevent another occurrence of sole pilot murder-suicide - or a hypothetical where both pilots have suicidal intent - or when a single pilot is incapacitated while the other pilot is out of the cockpit for medical reasons or other reasons?
The problem being that while the reinforced cockpit door can be opened with an access-code, the occupant of the cockpit can countermand (indefinitely?) the access attempt. Has that policy been changed?
What safety-rule or practices are being instituted to protect against this - or is the pilot murder-suicide scenario being removed from the threat-model entirely? (so if I see one of the pilots banging on the cockpit door while in flight I should resign myself to my fate?)

The French accident investigation board, Bureau d'Enquêtes et d'Analyses pour la sécurité de l'aviation civile (BEA), investigated this incident. The report was completed in March 2016. Among the recommendations for EASA was better medical and psychological monitoring by the aero medical examiners. Explicitly not recommended was the already mentioned practice of the two person rule, which leads to the security door being open too many times.
An aero medical examiner recommended that the pilot should have been committed to a mental facility two weeks before the incident. This fact only surfaced during the investigation. So his mental state was detected but because of lax institutional rules, nothing happened. The report can be found at bea.aero.

"Explicitly not recommended was the already mentioned practice of the two person rule" – I looked at the report for a few minutes, and from what I saw, it looked like the two-person rule was recommended. Can you point out where the report recommends against this rule?

No, the two person rule was created as an intermediate solution. After the report came out, this was rolled back. One of the reasons was, that the cockpit door was left open longer and more often. This was undesirable.

Well, you write that the two-person rule was "explicitly not recommended," so I was hoping you could point out exactly where the two-person rule is recommended against.

This is a large part of the problem today: "the potential financial consequences generated by the lack of specific insurance covering the risks of loss of income in case of unfitness to fly" and BEA recommendation is "mitigation of the consequences of loss of licence". Someone pathologically anxious for their future is not going to provide an excuse for redundancy. Recognize problems are legitimate, encourage to tell about them instead of hiding them. That's a base of TQM and good management. Else nurses start hiding they broke a vaccine phial and inject water instead, as we have seen.


text:
Why the safety of airplanes have not been developed long time ago?
I have a question about the safety of airplanes.
since I was a kid the first time I flight by airplane they have the safety which is a belt and yellow thing that puts into your mouth when a problem happens. If we notice today we still have the same safety and everything is almost the same except the way they show you the safety so today we have screen in front of seats which shows how to do safety by video tape.
Now, what I want to know "why don't we improve the safety since that time like 20 years ago from now for example?"
If you say there is no way to improve safety I will tell you a hint about improving the safety of people when they are in the air and things is getting worse (we can think more to get more ideas about improving the safety of airplanes).

We can put in every seat or every 6 seats a paragliding emergency where if there is something happens to airplane and it goes down, then we can rescue the life of people. You can argue with me about how to do it but it is for sure necessary to put paragliding tools in every airplane we have in order to prevent the death of airplane accident, especially as the number of airplane accident is increasing, the death of people is increasing.

Don't agree with me that we need to improve the safety of airplanes to save people life. In these days, I always hear that airbus announces a new model of their airplane, but they only improve it to earn more money by putting more seats and using less oil!!
I hope to find someone specialliest in this airbus or any airplane and tell us why we still see the same safety that was in 20 years ago?!

The most effective way to improve safety in airplanes is not to load them up with equipment to be used in case of a crash (which often no concievable safety equipment could make survivable), but to make them more reliable, so they crash less often.  I believe a look at fatalites per million passenger miles will show this has been done.

Most safety improvements are things that passengers never see, a majority of it being crew training, and other things like structural changes. Even the design of the seat, materials used, fuel tanks, etc have all been greatly improved over the years, stuff that you wouldn't notice. The reason a seat-belt and oxygen mask are still used is that they are still effective, and supplement other safety measures.

By the way: "as the number of airplane accident is increasing, the death of people is increasing." is completely false. It is true that a single accident may kill more people (larger aircraft), but the number of incidents is going down year-over-year since the early 80's. Flying is safer than ever. Most of what kills people in crashes isn't the crash, its the fire afterwards...

@RonBeyer Yes, you are right, if they improve the crew training, then we have a high probability that airplane accident would be decreasing. I did not see this point. Thank you for your two helpful comments! Completely agree with you!

Can you provide proof for your claim that safety hasn't improved in the last 20 years? I'm pretty sure that there have been dozens of advisories, reports, suggestions, recommendations, ADs, etc. by the relevant authorities in that time frame, plus improvements the manufacturers made by themselves without being prompted or forced by the authorities, plus improvements in reliability, plus improvements in training, plus improvements in procedures, and many, many, many things more.

For example, as a result of the Überlingen Mid-Air Collision of 2002 (so, well within your 20-year time frame), 2 changes were made: 1) a strict policy that pilots should always follow TCAS RAs and ignore ATC, 2) development of a new TCAS version which is currently being phased in, that is able to reverse an RA if it detects that the other aircraft is ignoring its RA. There were also changes being made that ensure that there are always at least 2 controllers in the control room at all times. So, that's two improvements to safety procedures and one improvement to safety software.

We can put in [...] a paragliding emergency where if there is something happens to airplane and it goes down, then we can rescue the life of people.

There are some conditions in Air liners that prevent the save use of a parachute:

Height

atmosphere pressure
Air Liners cruse in heights where the atmosphere is so thin that you can't  get enough oxygen by normal breathing.  For this reason the planes cabin is under pressure. in consequence it is not possible to open the windows as escape.
Operating the parachute
Even if that was possible you have to fasten your self in the parachute harness. This is (depending on the  harness structure) difficult for an untrained person when standing on solid ground and IMHO impossible in free fall.
anoxia
You might blackout bye anoxia before fixed yourself in the parachutes harness.

Speed
Airliners cruse at 800+km/h (relative to the surrounding air). That means that you get decelerated by approximately 800km/h as soon as you leave the aircraft. This exposes you to huge forces resulting in serious injuries.
Landing a Parachute
Landing a parachute is dangerous for many reasons. In easy cases you fall into flat ground where you ma get minor injuries like a broken leg or similar.
But imaging to fall into a big tree, a lake or into rocky setting?  Do you think an untrained person can survive this without serious threads for her live?
Dangerous flight phases
Parachutes will only be useful above a minimum height. This minimum height does not only depend on the parachutes technical parameters but also on the time to get one, put it on and leaving the air plane for the slowest passenger. But the most accidents with fatalities happened during start or landing where was not time to leave the plane.
Likeliness of Survival
History shows that most accidents happening in the air can be handled by the crew and the plane can be landed (more or less) safely as long as it is in "one piece".
If the plane breaks into pieces in the air this usually  happens in a kind of "blow up" so that there is not time to look for a parachute and put it on.

So after all: No, having a parachute for each passenger will not improve their safety, it will only increase the overall weight of the plane.

I agree with what you said and I understand the results of using emergency parachute. I hope in future we have a physical things to save people life. Thank you for your answer! It is very informative!

800 km/h isn't a deceleration, it's a velocity.

What I meant is that the difference in speed is approximately 800km/h. I'm not a native speaker but I think that the sentence can be understood this way.


text:
Is there an engine database that would include information on number of HPT blades per engine?
I am attempting to compile information on the number of high-pressure turbine blades across a wide range of turbine engines. Currently, I have only been able to find this information through brut force searching and I wanted to know if an engine database with this type of granular information exists?
Additionally, I have searched through Jane's but wasn't able to locate the appropriate information.
Thanks in advance for any help.

So... you're looking for a database of information to populate a database of information? Make sure you have the appropriate permission to appropriate their data into your database...


text:
What fuel would a Bell Huey helicopter use in 1964?
What type fuel would a Bell Huey have used in 1964? If that matters, let's say for a medical evacuation situation

Uh...what it normally uses.

In 1964, the Huey would use JP-4 or JP-5 .
When fitted with models T53-L-5 or T53-L9, the Huey would burn JP-4.
With engine variety engine T53-L11 it would burn either JP-4 or JP-5. The JP-5 type fuel was mainly used for Navy operations.


text:
When is most of maintenance data collected
During which phase of flight is most of the maintenance data collected? Ascend, cruising or descend? Is there a website where I can find such information?

Aren't data monitored from engine start to engine stop?

Yes. But when is the main/critical maintenance data collected?

An example of such data might help to understand. I think critical parameters are permanently monitored, e.g. vibrations are continuously monitored, not only when thrust is maximum (takeoff). Or do you mean: During which phase abnormal values do mostly occur?

Are vibration parameters considered maintenance data? Because you said that they require real-time monitoring and I don't know if they can be considered maintenance data.

You may want to read this.

Are you only interested in engine data or other data as well?

Any data. In fact, the more data I know of, the better.


text:
How can shifting to TCP/IP make current aviation systems more delay-tolerant?
I've recently been reading a number of articles on the current aviation systems. Many of them say that the current aviation infrastructure is 'inefficient' since it is based on OSI model and, so, Eurocontrol/FAA are trying to shift to a TCP/IP model (without further elaboration as to why it is inefficient.)
As far as I know OSI and TCP/IP are both protocol stacks and pretty much follow the same ideas.
I'm not quite sure why they say that the current OSI model is inefficient? In what sense is it inefficient?
Another point, in the articles I read, which I thought was a bit vague, was that it said that the TCP/IP model is more 'modular' and can improve 'flight delays'.
Again, weren't both OSI and TCP/IP models created to make systems more modular? How can shifting to TCP/IP make current aviation systems more delay-tolerant given that the main cause of delay is air traffic and weather?
Articles I've read.

This one is the main article, published by Eurocontrol/FAA, that I read. It suggests a transition from a voice-based to data-based services network.
This one is a PhD thesis. See Section 3.1 for the main references. They refer to the TCP/IP ATN as ATN/IPS. Search for the word 'ATN/IPS'.
This one gives a detailed description of ATN/IPS.
The following claims that a TCP/IP model is more modular than the current OSI based model.

Could you post a link to this article?

On a side note, TCP/IP is one of the layers (4) in the OSI model, so I'm not quite sure what their analogy is trying to say without reading the article itself. Unless they are referring to this (DARPA model), which is essentially the same as the OSI model - https://technet.microsoft.com/en-us/library/cc958821.aspx

The OSI model is a generic conceptual model for understanding data movement in telecommunications systems. It's an educational tool, not something you could implement. This question doesn't make sense I'm afraid.

https://www.eurocontrol.int/sites/default/files/field_tabs/content/documents/communications/cocr-future-radio-system-v.2.pdf

From my understanding, they are trying to transition from traditional voice based ATC services to data based services and, "because of this" (as they reason), ICAO is trying to standardize an Aeronautical Telecommunications Network (ATN) based on the Internet Protocol suite. This so-called ATN/IPS is intended to replace the existing ATN, which is based on the ISO/OSI protocol stack.

Neither OSI nor TCP/IP are mentioned in the report you linked to in your comment, at least they aren't in the abbreviations list and the Find function doesn't find them. Can you edit your question to add a link to the report and some actual quotes from it to help explain what you're reading?

I edited my question.


text:
What and where are "flotation seat cushions"?
Inspired by the question Why did the US Airways Flight 1549 passengers stay on the wings?
I read parts of the respective accident report[PDF]. They mention the flight was a
non-EOW (extended overwater) flight but was luckily equipped as such anyways and thus had life vests and
"flotation seat cushions".
Section 2.10.3.3.1 "Equipage" of the report states

Because the accident airplane was equipped for EOW operations,
  it carried life vests for both passengers and crewmembers.
  However, given that the accident flight route was not an EOW
  operation, the airplane could very well have been equipped
  with only slides and flotation seat cushions as the primary
  means for passenger flotation.

I've never heard of such a device, I only know the life vests below a
passenger's seat. Can the seat cushion (the part where you sit on, I assume)
be detached from the seat to serve as a "swimming aid"?
Maybe it's different in the US and Europe. I sometimes fly from Germany to the UK
and the FAs never mentioned any cushions. How comes?

It became something of a meme:

In the unlikely event of a water landing, your seat cushion can be used as a flotation device.

You remove your seat cushion and hold the straps on the back as a flotation device. It's probably more of an aircraft/airline thing than by country. It seems that the industry is favoring life vests more, as they are designed to keep a person afloat and face up even if unconscious and not adding the requirements to the cushion allows the seat to be smaller and lighter.

Source

To add to fooot's answer, emergency equipment required on aircraft varies based on the routes the aircraft will take.
In the most extreme case, if the aircraft will be performing Extended Over-water Operations (EOW), then it requires rafts, life vests, and more:

14 CFR § 121.339 - Emergency equipment for extended over-water operations.
a. Except [... ] no person may operate an airplane in extended overwater operations without having on the airplane the following equipment:

A life preserver equipped with an approved survivor locator light, for each occupant of the airplane. -- that's a life vest

Enough life rafts (each equipped with an approved survivor locator light) of a rated capacity and buoyancy to accommodate the occupants of the airplane. Unless excess rafts of enough capacity are provided, the buoyancy and seating capacity beyond the rated capacity of the rafts must accommodate all occupants of the airplane in the event of a loss of one raft of the largest rated capacity.

At least one pyrotechnic signaling device for each life raft.

An approved survival type emergency locator transmitter. [...]

[...]
c. A survival kit, appropriately equipped for the route to be flown, must be attached to each required life raft.

If the aircraft will go over water, but to for "extended over-water operations", then the requirements are lighter:

14 CFR § 121.340 - Emergency flotation means.
(a) Except as provided in paragraph (b) of this section, no person may operate an airplane in any overwater operation unless it is equipped with life preservers in accordance with § 121.339(a)(1) or with an approved flotation means for each occupant. This means must be within easy reach of each seated occupant and must be readily removable from the airplane.

And if it does not go over water at all, or very very shallow water only:

(b) Upon application by the air carrier or commercial operator, the Administrator may approve the operation of an airplane over water without the life preservers or flotation means required by paragraph (a) of this section, if the air carrier or commercial operator shows that the water over which the airplane is to be operated is not of such size and depth that life preservers or flotation means would be required for the survival of its occupants in the event the flight terminates in that water.

Depending on the airline and its routes, they may have all their aircraft equipped for EOW anyway (added cost but more flexibility), or only part of them for EOW and the rest for other overwater operations, or only the latter.
Extended overwater operations are defined as:

with respect to aircraft other than helicopters, an operation over water at a horizontal distance of more than 50 NM from the nearest shoreline.


text:
How come some aircraft have really cool registration numbers?
I've seen registration numbers like

D-ICEY - A Cessna Citation owned by a German company that produces frozen foods
G-FILM - An Alouette II helicopter used in some movies and TV series for the flying sequences

and Aviation Humor, for example, lists many other examples like TF-MOM, TF-DAD, TF-SON, TF-KID (all of former WOW Air).
I imagined it might work similar to how license plates for cars are issued in Germany (I know it's different in other countries): Here the first one to three letters are determined by the town/area you live in (e.g. F for Frankfurt). The remaining part is more or less random but you can pick from a list of these random numbers (for a fee of around 20 €).
Does it work the same with aircraft registration numbers and those people simply were lucky because e.g. D-ICEY was still available?

The first letter (s) before the dash are country code.

@Sanchises Yes, I'm aware of that. D for Djermany (kidding), G for Great Britain. But what about the part after the dash?

@PerlDuck D is for Deutschland if you don't actually know

@J.Hougaard Of course I know. But if you say Germany aloud it appears to start with a D as in Djermany :-) I was just kidding in the above comment.

@PerlDuck Figured that was probably the case ... but hard to decode humor on text :D

Aircraft registration numbers are assigned by the country where the aircraft is registered. Each country has a prefix (see the full list on Wikipedia), like e.g. D- for Germany. The prefix is usually separated from the rest by a dash, but some countries deviate from this, most notably the United States, where registration numbers begin with N.
Whether or not custom registration numbers are available depends on the country. In Germany, the authority in charge of assigning registrations is the Luftfahrtbundesamt. It is possible to ask for a custom registration number via the form Antrag auf Vormerkung eines Kennzeichens (§ 19 Abs. 2 LuftVZO). The fee is currently 30 Euros. In order to get the custom registration, it must be available of course, but also follow these rules:

D-AAAA to D-AZZZ for aircraft with more than 20 t MTOW
  D-AUAA to D-AZZZ (test registrations) for aircraft manufactured by Airbus at Finkenwerder
  D-BAAA to D-BZZZ for aircraft with 14–20 t MTOW
  D-CAAA to D-CZZZ for aircraft with 5.7–14 t MTOW
  D-EAAA to D-EZZZ for single-engine aircraft up to 2 t MTOW
  D-FAAA to D-FZZZ for single-engine aircraft from to 2–5.7 t MTOW
  D-GAAA to D-GZZZ for multi-engine aircraft up to 2 t MTOW
  D-HAAA to D-HZZZ for rotorcraft
  D-IAAA to D-IZZZ for multi-engine aircraft from 2–5.7 t MTOW
  D-KAAA to D-KZZZ for powered gliders
  D-LAAA to D-LZZZ for airships
  D-MAAA to D-MZZZ for powered ultralight aircraft
  D-NAAA to D-NZZZ for non-powered ultralight aircraft
  D-OAAA to D-OZZZ for manned free balloons
  D-0001 to D-9999 for gliders.

So it was at least in part luck that D-ICEY was available and fit the rules for a Cessna Citation.
In the UK, the authority in charge is the Civil Aviation Authority (CAA), which also allows custom registrations (called out of sequence here). The fee is currently £158.
This answer explains the procedure for the US and Canada.

So it's basically the same as for cars: take what they offer or pick one from a list (for a fee). Thank you. /// Btw, in particular that D-ICEY got my attention because just a few weeks ago it happened to overrun the runway here at the nearby EDFE and has torn down a fence 200 metres past the rwy. No pilot was harmed during this incident (I cannot tell for animals, though).

@PerlDuck Some countries allow picking anything that fits the rules and isn't already taken by someone else, not just picking from a short list of random choices as you describe.

@StephenS To be honest, the way you describe is exactly how it works in Germany for cars. I simplified a bit. Usually you say "I'd like to have my name's initials, e.g. PD" and then they show you a list of what's free with the letters PD in it, given "PD" fits the rules. Your initials, for example, would not be allowed for German license plates. Or you say "I want to end it in 3000" and then they show you a list of those that end in 3000. Often they have a website and you can "play", check, and even reserve a number in advance.

@PerlDuck Interesting. Most US states allow you to specify the entire string, so I could get "STEVE" or "STEPHEN" if I wanted, and are not bound by the current pattern in use for sequential plates..


text:
What's the acceleration and absolute minimal RWY length for an A320 during take-off?
TL;DR: An A320 takeing-off with full thrust is able to reach $V_{TO}$ (77 m/s) in only 26 seconds and in as few as ~ 1.000 metres. Is that really true?

Last time I traveled with an A320 I was again impressed by the acceleration during takeoff. I think it's not outstanding (compared to others) but nonetheless impressive. A cause might be that passengers are somehow exposed to the powers and cannot influence it. But I enjoyed it and it made me doing some calculations.
I gathered the following data:

usual take-off speed $V_{TO}=150$ knots (source)
required runway length $2000 \text m$ (source)
max. thrust per engine $\approx 120 \text{kN}$ (source)
MTOW $78 \text{tons}$ (source)

For constant acceleration along a path the following rules apply:
$$\left.
\begin{array}{}
s = \frac{1}{2} at^2 & \Leftrightarrow & t = \sqrt{ \frac{2s}{a} } \\
v = a \cdot t        & \Leftrightarrow & t = \frac{v}{a}
\end{array}
\right\}
\Rightarrow
a = \frac{1}{2}\frac{v^2}{s}$$
With the data from above this gives an acceleration from 0 to 100 km/h (or 62 mph or 28 m/s) in approximately 18.5 seconds and about 52 seconds for reaching the take-off speed. That sounded a bit lame compared to my 100hp station wagon.
So I investigated further, this time from Newton's point of view, $F=ma$, which gives an acceleration of $a = \frac{2 \cdot 120.000 N}{78.000 kg} \approx 3 \frac{m}{s^2}$. That gives 0…100 km/h in about 9 seconds. This far better coincides with my gut feeling as a pax.
But my second approach, $a \approx 3 \frac{m}{s^2}$, also resulted in the following conclusion and question:
An A320 takeing-off with full thrust is able to reach $V_{TO}$ (77 m/s) in only 26 seconds and in as few as ~ 1.000 metres. Is that really true? I was amazed at this because they all say the required RWY length is twice as long.

"For constant acceleration along a path the following rules apply" - okay, but what about non-constant acceleration? Aircraft get fast, and fast means more drag, and more drag means lower acceleration per thrust force unit.

That's exactly my dilemma. Constant acceleration says 18.5 secs from 0 to 100 km/h while Newton says 9 secs. But when I read @ ymb1's answer, it's even worse, given the drag and tyre friction.

78.9T is a bit much, and in fact over MTOW on most A320s. Shortest runway we can operate per manual is 1600m. We have DOW routinely into the ~53-55T, so assuming an empty a/c with very little fuel, optimum flaps config and TOGA thrust, I assume as little as 1000m would be enough. Mathematically. There is a lot of extra safety margin to account for various scenarios (net vs gross engine performance, wind change, weight&balance errors) so you will end up with a much larger required take off run

What about wind? Given enough wind, takeoff acceleration time can be exceptionally short.

A320 airborne in less than 800 meters.  https://youtu.be/im32AHm0qq8

"the required RWY length is twice as long." Yes, because in the event of an aborted takeoff they need to be able to decelerate to a stop (which will take roughly the same distance) before reaching the other end.


text:
How dangerous would it be to take off at night with no ATC, no runway lighting system and have a single engine working?
I was wondering how dangerous it would be to  have an engine failure (with a twin-engine) during take off at night when you have no runway lights (and no city close-by) and no ATC?
Would using the aircraft flight instruments alone be considered IFR?
Thanks

No, it would not be considered IMC.

I was wondering how dangerous it would be

When you preface a question with the above, you're asking for opinion, and when it comes to the details of what you ask, there will be widely differing opinions. That said, and in the context of the U.S., and if I understand your question (apologies if I'm misreading), the details of your question break down into three separate areas. One can come up with a number of possible scenarios which might combine those details, but let's use a concrete instance to better explain. I at one time was the company pilot for a firm that manufactured and maintained computerized sawmill equipment at mills throughout the west coast of the U.S. If one of our computerized systems broke down, we would fly to the mill as soon as possible. Some of these mills had private airfields alongside the mills or nearby. We could not reach ATC on the ground from any of them, and most had no runway lighting. Typically we would go into an airfield during the day, and often it would be dark by the time we completed repairs and left.

no ATC

All night flights were done IFR. We would get an IFR clearance over the phone with a "void if not off by" time. So you takeoff, abiding by the clearance, and contact ATC on the assigned frequency as soon as you have enough altitude to reach them.

take off at night when you have no runway lights

As long as you have landing lights and are familiar with an airfield, the lack of taxiway and runway lights is not a significant problem. What is a problem at remote runways is the possibility of animals (usually deer) on the runway, which is why we typically had at a car precede us down the runway while flashing their lights and honking.

an engine failure (with a twin-engine) during take off at night

The twin engine aircraft we had available were a Cessna 310 and later a King Air A90. Unlike air carrier airplanes, continuing the takeoff if an engine failed during the takeoff roll was not an option, but the probability of that happening wasn't affected by time of day. Day or night, the only option was to abort. We were no more exposed during the night than during the day in that respect.
If an engine failure happened after takeoff, day or night, you would handle it in the same way. Fortunately, we were operating out of airfields where our departure path wouldn't need to be altered due to the reduced single-engine climb rate.
We had a single-engine Cessna Turbo 210 available as well. During the time that was our primary aircraft, we had no qualms about single-engine night or IFR operations. Many may disagree with such. However, although as I remember Part 135 of the FAA regs does not allow single-engine night or IFR, Part 91 does (or at least did) and I never personally knew anyone who had problems while doing so. Obviously there is some additional risk, but we considered that acceptable.


text:
May a Cessna 182 land on a major, high-traffic airport, say EDDF (Frankfurt)?
Some 30 years ago a family's friend owned a TR-182 Skylane (Turbo,
retractable gear) and we sometimes flew around here in the Rhine-Main
area around Frankfurt. Of course he used EDFE (Egelsbach) for take-off
and landing. I remember asking him if it would be possible/legal to land
in Frankfurt with his Cessna 182.
As I recall, he said they would likely reject such a landing as they
wouldn't really appreciate us occupying a runway and make the big planes
wait for our tiny one. Even if we were allowed, the landing and parking
fees would be in such high regions that no one in their right mind would
be willing to pay them.
The only exception, he said, would be an emergency. In that case we
could very well land in Frankfurt but must be prepared for massive
interrogation afterwards if the emergency wasn't obvious.
I'm not asking about a C182 specifically but about "small" GA planes
(say MTOW below 2-3 t) on "big" German airports such as Frankfurt.

Related for USA: Can you fly a light GA airplane into a major hub? What operational considerations are there if you do?

Note that most of the answers to that question are US-centric. In many other countries, light aircraft are banned from major airports, or the fees are so high that they might as well be.

There is the General Aviation Terminal (GAT) in Frankfurt that is handling "executive and private aviation flights" as they say. General aviation airplanes and helicopters are handled at this GAT that is open 24 hours per day. I think the best is to contact them.
Some additional rules related to GA in Frankfurt can be found here. Bus service is mandatory for passengers between aircraft and GAT. The list of services includes a sentence Lashing of small aircraft. So probably some not very big are expected to arrive.
Landing fees in this airport are used solely to refinance airport infrastructures and the resulting operating expenses. They are regulated, and, while not exactly very cheap, they are not astronomic either.


text:
Are measures taken to deliberately increase the fuel burn rate to lower the landing weight?
Just recently the Air Canada flight AC837 from Madrid to Toronto had problems with the gear right after take-off and they decided to abort the flight and go back to Madrid. It was a B767-300 (C-GHOZ) which, AFAIK, cannot dump fuel so they circled approximately four hours southeast of Madrid in order to burn the fuel before landing:

(Source: Flightradar24, https://www.flightradar24.com/data/flights/ac837#23be1953)
Four hours is quite a long time and I wonder if the pilots actively do something to increase the rate at which fuel is burnt to somehow speed up the whole process. Like running the engines at full thrust and/or putting speed brakes/flaps in place. I don't know if they retracted the gear (which dramatically decreases the fuel consumption), but I doubt so because its damage was the whole reason for the circling.
If it matters: they circled approx. 1h @4500 ft and then approx. 2h 45m @7500 ft before heading back in Madrid.

Yeah I'd say so.

This is a good case illustrating the possible dupe. If not understood as a dupe, it can be understood as "what are the measures taken in this specific occurrence?"

@ManuH I agree it is a duplicate. I am not interested in the measures taken in this particular case, it merely triggered my curiosity. I haven't seen the other question. Sorry for the noise.

@JohnK So do I. I just VTC as dupe. Or is deletion the preferred action?

@PerlDuck as the OP, I believe your VtC will auto-close the question. Deletion isn't necessary


text:
How are aircraft lifespans tracked?
When returning from each flight, during which it is subjected to adverse conditions, say arctic weather, desert heat or just moderate conditions, how is an aircraft evaluated to accurately keep track of its lifespan?
If the method is a standard: "this aircraft has had "this many" hours of flight, & therefore, there are "this many" hours left for the aircraft before it is rendered not worthy for service" then this method doesn't consider the various conditions the aircraft is subject to during each flight, which impacts the aircraft's lifespan at varying degrees. I trust there is a more accurate method of evaluation (after each flight perhaps?)
Appreciate your asisstance in clarifying this doubt.

Which kind of aircraft are you asking for? General aviation, airliner, military?

Well all the above actually; but a good marker would be military i guess, since it is the most punishing line of work for an aircraft.

The life (Low Cycle Fatigue life) on the Civil airliners is generally talked abut in terms of number of cycles i.e. number of flights. And since airliners undertake quite predictable flights in terms of loads and stresses, and typically a very limited variations among these parameters for their entire life (since any aircraft would be designed for certain type of range and payload and would be used for that particular purpose mainly, for economic reasons), its easy to talk in terms of number cycles, since variations from flight to flight are limited.
But this issue of keeping track of actual mission profile is very critical for fighter (actually any military jet but I would restrict myself to only Fighters because its easier to point out the things for this case) jets which have quite unpredictable usage profile. Any fighter jet is typically designed for a certain mission mix i.e. mixture of a bunch of mission profiles that the fighter is expected to carry with the expected relative frequency (which comes from the past experience of an Air Force). But still in real life, the actual missions flown end up being quite different that this assumed mission mix. Now it is possible to utilize the airframe structural life to best possible extent by keeping track of actual mission profiles flown and debiting life for each mission from the designed number of hours. Obviously one needs to calculate the life debit for actual mission flown in terms of the equivalent hours for assumed designed mission mix. Say a fighter is designed for 8000hrs assuming it will fly 10 times of missions with certain frequency, and it recently flew a mission for which we know the parameter, then what would be the number of hours of equivalent life that was utilized from this 8000hrs..?
To calculate this we need the loading parameters of each mission such as how many Gs were pulled for how long time intervals, how many rolls performed with what roll rate and so on. Every aircraft has system which collects this information (measured by various sensors) for entire mission. Once on the ground, this information is fed to what is called as "Life Tracking System". It analyses the data, calculates how many hours of debit this mission took on the airframe and then decides what is remaining life.
This can be done at component level as well and one can keep track of available life of each component and accordingly schedule maintenance for each component individually. I am not sure how this is exactly done for entire aircraft (Looking for Patents by Aircraft OEMs would be a good way to start digging in), but I know for the Jet engines. The methodology should be the same in principle. Specifics might change. I suggest you read about Volvo Aero RM12 Life Tracking System (LTS) which finds its origin in GE's LTS for F404. (A good starting point to read) and another one. Essentially all OEMs have similar systems now. RM12 has improved utility of the engine by ~30% i.e. the engine is used for 30% more time now as compared to the case where LTS was not used and differences in missions were not accounted for. Because many missions do not take as much toll on the structural life as it was expected during design (or more number of less stressful missions are flown in actual practice than it was assumed for design).
Most popular technique used to calculate the equivalent LCF life debit for each mission considering variations in loads and stresses for each mission specifically is known as Rain Flow Counting Algorithm. The process essentially looks like this:

You apply the actual measured loads and see what stresses the analysis predicts for each mission. Then apply Rain flow Counting to calculate accumulated structural fatigue damage and residual life remaining. Rain drop counting is the model which helps you covert the irregular fatigue loading (i.e. varying missions) to equivalent cyclic loading and thereby coming up with a life debit number which is equivalent to the design mission mix and which you can subtract from the designed life hours. That's how you can take care of variation in the missions and loadings in each mission.

For civil airliners: flight cycles. The first aircraft is statically torn to bits to test the maximum strength, another aircraft will be the leader for fatigue cycles and will go through 5 minute flights, day in day out, year after year.
Here's a video on the static test of the A350. It shows the aircraft being strapped in and attached to actuators that bend the wing while measuring the forces on it. Distributed actuators to reproduce aerodynamic lift distribution.
The dynamic test aircraft goes through a tough test program:

Start of test: rumble the wings up & down to reproduce wing loads while taxiing
Higher amplitude shocks and slight bending upwards of the wing, to reproduce the load from the Take Off run.
A sudden jolt on the wing upwards, to reproduce the moment of take-off when all weight is supported by the wings.
A hissing sound: slow inflation of the fuselage, to reproduce climbing to altitude while maintaining pressure inside the aircraft. At the end of this inflation there is awesome creaking.
Some bending of the wings for the effects of fuel transfer, some turbulence, temperature changes when landing and the sun shines on the upper surface while the fuel at the lower surface is below freezing point of water.
Release of overpressure.
The landing jolt on the wing downwards, followed by more taxi rumblings.
End of test: only a couple of minutes after the start.

This is repeated a couple of hundred times a day, year after year, to become aware of fatigue problems. Cracks that show up stop the tests, then have the manufacturer issue bulletins on replacement of the cracked panel or beam.

Interesting video. Save yourself, though, and do NOT read any of the comments - they live up to the stereotypical YouTube comment level. :(

Yes some of the comments are atrocious. Always easy to pick on someone, isn't it.


text:
Considering a piston engined aircraft, what resistance pressure would be generated within its engine bay against its cooling intake?
Consider a piston engine with all its coolers and components within an aircraft engine bay. To cool this engine, cooling intakes are positioned facing the direction of flight. Now, the condition at the inlet surface need not reflect the flight conditions exactly, one reason for this would be since the resistance pressure from within the engine bay would influence the conditions at the inlet itself.
The question is specific to this resistance pressure as a first approximate at least. I know there are a variaty of other reasons as to why the conditions at the inlet surface would change (e.g pressure distribution at location of intake position, inlet type, etc...) but those aren't a concern here yet.
A good answer to this based on actual data, or statistical data or even experience would be greatly appreciated. Sources as to where one may find the answers to this would also be much welcomed. Thanks in advance!

I find my engine cooling works best in straight & level flight. Loss of cooling is seen in a climb. Cooling is also affected by how much the cowl flaps are open, or closed. And by how rich the mixture is set.  All in all, I try to keep the cylinder head temperatures at 380F or below for best cylinder life, using less severe climb, opening the cowl flaps more, enriching the fuel flow more (could be simple change from 10 gph to 11 gph at 2400 RPM for example), and reduced RPM.  I don't have a gage to measure air pressure directly.

3 main points come to mind:

The space above the cylinders is a pressure plenum so that the air pressure and velocity flowing past the cylinders is the same everywhere.
The space below the cylinders is a low pressure zone and to achieve that the exhaust opening should be larger than the inlet opening(s) to get the highest differential at low speed, but can be reduced as ram pressure increases (hence a cowl flap).  The pressure balance has to take into account air bled off the high pressure plenum to pass through coolers or other services that need ram air.
The baffling that controls the flow between the high pressure plenum above to the low pressure exhaust zone below past the cylinders has be tight to the cylinders, actually touching the fins, so that the cooling air is forced between the fins.  Cooling air that passes beyond the edges of fins does no good.

As for details and numbers, you should probably obtain this book on piston cowling design.

Well my question considers the engine and all its coolers and components within the engine bay as a single package, and the resultant pressure resistance it generates at the cooling intakes is what I'm looking for. I would think it would have to do with the density and temperature within the engine bay as a result of the engine running. Considering this as an incompressible case, I still don't have the temperature in hand at the moment to calculate an estimate number. If there is a rough figure or guide on this, I would appreciate it.